The present invention is directed generally to a liquid seal for maintaining pressure differentials between various parts of an apparatus. In particular, to a seal that provides for defining separately controlled vacuum zones. The low gas conductance seal is mechanically robust and is designed so that mechanical vibrations cannot be transmitted through the seal.
Quite often, within an apparatus, such as a piece of processing equipment, it can be desirable to define zones having different pressures and to maintain these differential pressures for extended periods of time. There are various ways of accomplishing this separation such as by the use of physical structures or barriers that act to seal one region of the apparatus from another. In systems that operate at sub-atmospheric pressures, these zones can be maintained by means of differential pumping, i.e., having separate vacuum pumps to control the pressure-within the various regions. In addition to establishing zones or regions having different pressures, it can also be necessary in some applications to minimize or substantially eliminate vibration transmission from one zone or region to another.
Seals capable of creating zones of different pressure within a vacuum system while at the same time transmitting negligible or substantially no vibration are particularly desirable for applications such as Extreme Ultraviolet Lithography (EUVL). Here Extreme Ultraviolet (EUV) radiation (10-14 nm) is used to produce features having linewidths less than 100 nm. Because of the very fine dimensional tolerances (.apprxeq.10s of nm) involved in EUVL low vibrational transmission is an absolute necessity. It can also be desirable to have a seal that can operate with pressure differentials up to 0.5 Torr while at the same time having negligible gas conductance. Moreover, it can also be desirable to have a mechanically robust seal that can maintain its structural integrity. It can be necessary to clean the inner surfaces of the vacuum system from such things as carbon deposits. This cleaning operation is frequently done by rf-discharge cleaning, wherein reactive oxygen species are introduced into the vacuum system. Thus, it is further desirable that the zone seal be resistant to reactive ion species used for cleaning the vacuum system.